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1
Chapter 1. INTRODUCTION
1.1 Research Needs and Significance
Chip seals are one of the most common preventive maintenance treatments used in the
United States (Gransberg et al. 2005). A chip seal consists of a thin layer of asphalt concrete less
than one inch thick formed by the application of emulsified asphalt and aggregate, with the
purpose of sealing the existing pavement’s surface cracks, improving ride quality, and
rejuvenating the surface against aging or oxidation. A chip seal provides a durable and functional
pavement surface that serves as a highly economical highway maintenance option when
constructed properly. For example, in North Carolina in 2006, approximately 8% of roadway
pavement expenditures were spent on surface treatment construction. That percentage constitutes
about 50% of the road miles paved in the state. Thus, it is imperative for state highway agencies
to optimize the use of these treatments through prolonged service life, decreased life-cycle costs,
increased operational efficiency, and enhanced safety. Typical chip seal failure modes include
aggregate loss, cracking, bleeding, reduced skid resistance and aging, among others. It must be
noted that aggregate loss is a serious concern in chip seal construction because flying aggregate
may create windshield damage to a vehicle (Gransberg et al. 2005) or other serious harm. This
problem discourages the use of chip seals on high-volume roads (Shuler 1991).
Chip seals constructed with polymer-modified emulsion (PME) provide better initial and
long-term performance and extend the overall service life of pavements (Crew 2008). The use of
polymer-modified chip seals, which have tougher, more resilient surface characteristics
than unmodified chip seals (AEMA 2004), may extend the use of chip seals to roadways that
have a higher traffic volume than the low traffic roadways for which unmodified chip seals are
typically used.
The enhanced performance and benefits of chip seals constructed with PME can be seen
in the following:

1
Chapter 1. INTRODUCTION
1.1 Research Needs and Significance
Chip seals are one of the most common preventive maintenance treatments used in the
United States (Gransberg et al. 2005). A chip seal consists of a thin layer of asphalt concrete less
than one inch thick formed by the application of emulsified asphalt and aggregate, with the
purpose of sealing the existing pavement’s surface cracks, improving ride quality, and
rejuvenating the surface against aging or oxidation. A chip seal provides a durable and functional
pavement surface that serves as a highly economical highway maintenance option when
constructed properly. For example, in North Carolina in 2006, approximately 8% of roadway
pavement expenditures were spent on surface treatment construction. That percentage constitutes
about 50% of the road miles paved in the state. Thus, it is imperative for state highway agencies
to optimize the use of these treatments through prolonged service life, decreased life-cycle costs,
increased operational efficiency, and enhanced safety. Typical chip seal failure modes include
aggregate loss, cracking, bleeding, reduced skid resistance and aging, among others. It must be
noted that aggregate loss is a serious concern in chip seal construction because flying aggregate
may create windshield damage to a vehicle (Gransberg et al. 2005) or other serious harm. This
problem discourages the use of chip seals on high-volume roads (Shuler 1991).
Chip seals constructed with polymer-modified emulsion (PME) provide better initial and
long-term performance and extend the overall service life of pavements (Crew 2008). The use of
polymer-modified chip seals, which have tougher, more resilient surface characteristics
than unmodified chip seals (AEMA 2004), may extend the use of chip seals to roadways that
have a higher traffic volume than the low traffic roadways for which unmodified chip seals are
typically used.
The enhanced performance and benefits of chip seals constructed with PME can be seen
in the following: